In a rapidly shrinking business world, use of facsimile transmission of documents and the like is increasing at a rapid rate worldwide. The introduction of digital networks and the use of high resolution monitors for soft copy and browsing have added additional requirements to the facsimile world. For some applications, rapid output to a high resolution image is frequently desirable and sometimes necessary. To this end, a number of arrangements have been proposed for enhancing received two-tone images in order to increase their resolution through use of progressive coding. In one particular facsimile progressive coding scheme, the image information to be transmitted is separated into so-called lower resolution information and supplemental information. In this prior facsimile scheme, the lower resolution information is based on a subsampling technique of the original image and the supplemental information is transmitted by employing a predictive encoding scheme based on the adjacent transmitted pixels (picture elements) of the image. One such prior progressive coding scheme is described in an article entitled "Progressive Coding Scheme for Interactive Image Communications", by T. Endoh and Y. Yamazaki, in IEEE Communications Society, Global Communications Conference, Nov. 26-29. 1984, pages 1426 through 1433.
A disadvantage of this prior facsimile progressive coding scheme is that excessive information is required to be transmitted when an image includes no information, for example, when an image has large areas of a single tone(i.e., either white or black). Also, if the subsampling interval is large, then thin lines can disappear completely. Other facsimile image coding schemes avoid this problem, e.g., see U.S. Pat. No. 4,261,018 issued to K. C. Knowlton on Apr. 7, 1981, by using some form of pyramidal data structure. However, such prior schemes require storing of the entire image to be transmitted and, consequently, require large memory. Additionally, such prior schemes are incompatible with the line-by-line coders which have been proposed as the standard for conventional digital facsimile transmission.